Grid structure for vapor electric devices



Apnl 14, 1936.' D. c. PRINCE 2,037,533

I GRID STRUCTURE FOR VAPOR. ELECTRIC DEVICES Filed March 30, 1931 miumummm Nil- [Ill/11111111171;

-Trllllllil7 A Inverfinor: David C. Prince,

by W Wm His Attorney.

. UNITED STATES PATENT OFFICE GRID STRUCTURE FOR VAPOR ELECTRIC DEVICES David 0. Prince, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 30, 1931, Serial No. 526,187

3 Claims.

My invention relates to vapor electric devices, such as the mercury arc rectifier or inverter, which are provided with anodes having grids associated therewith, and has for its principal ob- 5 ject the provision of an improved grid structure for such devices.

It is well known that in many instances the operation of the mercury arc rectifier or similar vapor electric devices is improved by the employment of grid structures to reduce the ionization in the neighborhood of the anodes, or tointerrupt long paths of electrons or for other purposes. Grid structures having surfaces which extend parallel to the direction of the arc stream in the vapor electric device have been found particularly useful for these purposes. Various forms of such grid surfaces have been used, the grids being usually constituted either by a grating or by a series of concentric rings or cylinders.

Difficulties have been encountered, however, in the use of grid structures of the above cited grating type and of the concentric ring type due to the fact that an arc stream at fairly low densities appears always to choose one path through the grid rather than to distribute itself between several parallel paths. The are stream thus tends to flow through one hole only in a grid of the grating type, or through the annular opening between one pair of adjacent rings only in a grid of the concentric ring type. While it is true that as the current is increased the are droprises and the are therefore tends to divide between the various passages in these grids, nevertheless some reluctance, tending to prevent proper distribution of the are through the grid, is always present due to the lack of ionization in those passages through which the arc has not previously flowed.

In accordance with my invention these diiiiculties are overcome by constructing the grid member in the form of a spiral instead of in the form of a grating or of a series of concentric rings, the turns of the spiral being maintained in proper relative positions by small spacers around which the arc stream can easily pass, the resulting grid structure providing a substantially continuous opening for the arc stream.

My invention will be better understood from the following description when considered in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a fragmentary sectional view of a vapor electric device in which my invention has been embodied, and Fig. 2 is a perspective view of the grid structure incorporated in the vapor electric device shown in Fig. 1.

In the drawing the vapor electric device [0 includes an evacuated tank I I and a plurality of anodes i2, only one of which is shown in the figure, each mounted within an anode chamber l3. In order to reduce ionization in the neighborhood of the anode l2 or for other purposes, a grid I4 is mounted below the anode, preferably on a shield member I5 which surrounds the anode, the grid having conductive surfaces parallel to the direction of the arc stream in the vapor electric device Hi.

In order to avoid the difficulties hereinbefore explained as due to the tendency of the arc stream to confine itself to a restricted path, the grid l4 comprises in accordance with my invention a conductive member or sheet I6 having a spiral form. The turns of the spiral are spaced by thin metal members I! which have little or no effect on the direction of the arc stream through the grid. Since the space l8 enclosed by the spiral plate or sheet [6 thus constitutes a substantially continuous opening for the arc stream through the grid, this opening extending at progressively greater distances from the center of the grid, no region exists in the grid which cannot be reached by a continuous spread of the arc stream after the stream begins to flow through any portion of the grid. Therefore the full area of the arc stream path occupied by the grid is available for the flow of the arc stream, which will therefore spread across the grid opening l8 progressively and not in the series of impulses characteristic of these grid types in which the arc stream is forced to flow through a plurality of openings arranged in parallel relation.

What I claim as new and. desire to secure by Letters Patent of the United States is:

1. In a vapor electric device including an anode and an anode shield surrounding said anode, a grid connected at one extremity thereof to the inner surface of said shield and extending spirally across the entire path of the arc stream in said shield, said grid member having oppositely disposed wall portions extending a substantial distance parallel to the direction of the arc and forming a continuous opening for said are stream through said grid, said opening at all points thereof being of sufiicient width to cause said arc stream to spread progressively across said are path from any point of the area occupied by said grid to all other points of said area.

2. In a vapor electric device including an anode and an anode shield surrounding said anode,

a grid connected at one end thereof to the inner surface of said shield and extending a substantial distance parallel to the direction of the arc stream in said device, said grid extending across the entire path of the arc stream in said shield and being Wound spirally to form a continuous opening through said grid extending at progressively greater distances from the center line of said shield to the inner surface of said shield, the adjacent turns of said spirally Wound grid being spaced apart a sufficient distance to cause said are stream to spread progressively across said entire ar-c path from any point of the area occupied in said shield by said grid.

3. In a vapor electric device including an anode and an anode shield surrounding said anode, a grid connected at one end thereof to the inner surface of said shield, said grid extending across the entire path of the arc stream in said shield and extending a substantial distance parallel to the direction of said are stream, said grid being Wound spirally to form a continuous opening through said shield for said are stream, the adjacent turns of said grid defining an opening of such width that said arc stream is caused to spread progressively and uniformly across said entire arc path from any point of the area in said are path occupied by said grid to all other points of said area.

DAVID C. PRINCE. 

